The overall objective of this proposal is to use functional MR brain imaging (fMRI) to better understand the neural circuits that contribute to problems with impulse control in Tourette's syndrome, Obsessive-Compulsive Disorder (OCD), and Attention Deficit Hyperactivity Disorder (ADHD). Clinical experience has shown that children who suffer from almost any serious developmental disability suffer most not from their primary diagnostic symptoms, but from their difficulties with impulse control, hyperactivity, inattention, and response inhibition. These associated problems cut across most diagnostic domains and are the most frequent cause for clinical referral, and by understanding dysfunction in this circuitry we will be better able to design and assess the effects of new therapeutics for these problems. We aim to understand better the neurobiology of these problems through the imaging of motor, attention, and inhibitory neural systems involved in impulse control in normal and developmentally disabled children. Our specific aims are: 1) To use fMRI to study the neural basis of impulse control in 80 normal children and adults (7-50 years old), and to compare the brain activity in these normal subjects with the brain activity in 80 TS, 40 OCD, and 40 ADHD subjects. 2) To study the functional connectivity of brain regions that subserve impulse control. 3) To show that task-related changes in fMRI signal can predict important behavioral measures in our models of impulse control. 4) To determine the effects that stimulant medications have on the activity of impulse control circuits in 40 children who have ADHD. 5) To develop and apply to the study of our models of impulse control new "event-related" fMRI task activation protocols in 40 normal and 40 matched TS children and adults. These studies should provide important new insights into the underlying neurobiological basis of each disorder.